After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.

Animals↗

PubMedDate not supplied

Toward an integrated continuum model of cerebral dynamics: the cerebral rhythms, synchronous oscillation and cortical stability.

Continuum models of cerebral cortex with parameters derived from physiological data, provide explanations of the cerebral rhythms, synchronous oscillation, and autonomous cortical activity in the gamma frequency range, and suggest possible mechanisms for dynamic self-organization in the brain. Dispersion relations and derivations of power spectral response for the models, show that a low frequency resonant mode and associated travelling wave solutions of the models' equations of state can account for the predominant 1/f spectral content of the electroencephalogram (EEG). Large scale activity in the alpha, beta, and gamma bands, is accounted for by thalamocortical interaction, under regulation by diffuse cortical excitation. System impulse responses can be used to model Event-Related Potentials. Further classes of local resonance may be generated by rapid negative feedbacks at active synapses. Activity in the gamma band around 40 Hz, associated with large amplitude oscillations of pulse density, appears at higher levels of cortical activation, and is unstable unless compensated by synaptic feedbacks. Control of cortical stability by synaptic feedbacks offers a partial account of the regulation of autonomous activity within the cortex. Synchronous oscillation occurs between concurrently excited cortical sites, and can be explained by analysis of wave motion radiating from each of the co-active sites. These models are suitable for the introduction of learning rules-most notably the coherent infomax rule.

Cerebral Cortex↗

PubMedDate not supplied

Current and future interests of National Institute of Child Health and Human Development.

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Diagnostic Imaging↗

PubMedDate not supplied

A new multigene family inducible by tobacco mosaic virus or salicylic acid in tobacco.

A previously undescribed cDNA family was isolated from tobacco challenged with tobacco mosaic virus (TMV). A cDNA library was constructed with mRNA from upper leaves of Xanthi nc tobacco plants that had been inoculated with TMV on the lower leaves 11 days previously. The library was screened differentially with radiolabeled cDNA synthesized with mRNA from upper, uninoculated leaves of either TMV-inoculated or mock-inoculated tobacco plants. The new cDNA family, designated SAR8.2, had at least five expressed members, one or more of which were inducible by TMV inoculation and by salicylic acid treatment. The cDNAs encoded small, highly basic proteins containing N-terminal hydrophobic signal peptides and highly conserved cysteine-rich C-terminal domains. One of the SAR8.2 family members contained a direct repeat of the C-terminal domain in tandem. Hybridization of SAR8.2 cDNA to tobacco genomic DNAs indicated a gene family of 10-12 members.

Amino Acid Sequence↗

PubMedDate not supplied